Electrodepositing black chromiumvanadium coatings and members therewith



Quaely, Montclair, N. house Electric Corporation, I corporation of Pennsylvania No Drawing. Application June 8, 1956 Serial No. 590,113

4 Claims. (Cl. 204-43) J., assignor to Westing- East Pittsburgh, Pa., a

- This invention relates to the electrodeposition of black coatingsof chromium and vanadium.

' This application is a continuation-in-part of my application Serial No. 339,469, filed February 27, 1953, now abandoned, and assigned to the assignee of the present invention.

It has been desirable to electrodeposit black coatings on members. Black coatings are desirable for decorative and similar applications, as for instance in making name plates and the like. However, there is a particular'need in'the electronic industry for black coatings that have adherence and stability when exposed to elevated temperatures especially under high vacuum conditions.

The object of this invention is to provide a process for electroplating on members a black coating comprising a complex of chromium and vanadium.

A further object of the invention is to provide members having an applied adherent black coating comprising a complex of chromium and vanadium.

Another object of this invention is to provide an electrolyte comprising an aqueous solution of a chromium compound, a vanadium compound and an organic carboxyl acid, such that black coatings may be electro-deposited from said electrolyte upon members.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

I have discovered a process for depositing novel black coatings on members, the coatings characterized by high stability and adherence to members even when heated to temperatures of 750 C. while in a vacuum. The process comprises the preparation of an aqueous electrolyte comprising essentially (a) from 150 to 385 grams per liter of chromic acid, (b) from 1.8 to grams of vana dium in a soluble compound thereof, the latter being supplied, for example, as from about 4 to 23 grams per liter of ammonium metavanadate, there being present from 100 to 9.5 parts by weight of chromium per part of vanadium, and (c) from 3 to grams per liter by weight of a water soluble carboxylic acid.

Exceptionally good results have been obtained from electrolytes containing 200 grams per liter of chromic acid (Cr a), and 20 grams per liter of ammonium vanadate. The ratio of chromium to vanadium in this electrolyte is 11.9 to 1.

The vanadium compound may comprise ammonium metavanadate, a vanadium halide or other vanadium compound soluble in water in the required proportions. Metallic vanadium powder or solid vanadium metal may be dissolved in concentrated nitric acid to produce asoluble vanadium compound for the purpose of the invention. Mixtures of two or more vanadium compounds may be employed in the electrolyte.

Examples of suitable water soluble carboxyl acids are acetic acid, formic acid, citric acid, oxalic acid and propionic acid and mixtures of any two or more thereof.

The aqueous electrolyte so prepared is disposed in an electroplating tank or cell, resistant to the action of chromic acid solutions. Glass, ceramic or rubber lined United States Patent tanks are suitable for this purpose. The electrolytic cell should be provided with suitable cooling means in order to maintain the temperature of the electrolyte within the range of approximately 30 C. to 50 C. Members to be plated are made the cathode in the cell while the anode comprises lead plates. However, carbon or graphite anodes or anodes of other insoluble materials commonly used in chromium plating may be employed. The memher to be plated will ordinarily comprise a metallic body, but other materials than metals may be plated after first applying thereto a conductive coating such, for example, as graphite or chemically precipitated silver. A potential of from 12 to 15 volts is applied between the cathode and theanode and a current density of from 400 to 2,000 amperes per square foot is passed through the cathode. The composition of thebath is maintained by the addition of the chromium and vanadium compounds as they become used up during the plating operation. by the bath though ordinarily the electrolyte is kept free of any extraneous additions.

The following examples illustrate the practice of the present invention:

Example I There was placed in a glass plating cell an aqueous electrolyte comprising 200 grams per liter of chromic acid (CIO3), 10 grams per liter of ammonium metavanadate, and 6 /2 milliliters of glacial acetic acid. A steel plate was-made the cathode in the electrolyte with a lead plate being the anode. An electrical current at a density of 900 amperes per square foot Was applied to the steel member. In 5 minutes plating, a black coating of a thickness of approximately 1 mil was deposited on the steel plate. The steel plate was then removed from the electrolyte and washed with water. The applied black coating was found to be very adherent to the steel plate. When heated in a vacuum to temperatures of 750 C., the color of the coating remained unchanged. When heated in an oxidizing gas flame, the color of the coating changed from a jet black to a gray black.

Example 11 An electroplating electrolyte similar to that of Example I was prepared. A copper anode-support such as is used in a rotating anode X-ray tube was made the cathode after having been previously cleaned to remove surface oxides. The copper anode-support was plated in the electrolyte at a current density of 1,000 amperes per square foot for 5 minutes. The anode-support was provided with a jet black coating of a thickness of approximately 1 mil. The anode-support was then assembled with the tungsten anode and was next placed in an X-ray tube which was thereafter sealed and evacuated. The tube was then put into operation and the anode rotated at a speed of 3,600 R. P. M. and subjected to an electron beam to produce X-rays therefrom. The coating was found to have a high thermal emissivity. The electrodeposited black coating was found to be highly adherent and unimpaired by longtime use.

Example III An electrolyte is prepared by dissolving 384 grams per liter of chromic oxide (CrO and 4.6 grams per liter of ammonium vanadate. To each liter of the solution is added 5 milliliters of glacial acetic acid. Adherent jet black coatings are electrodeposited on members by plating at current densities of 800 amperes per square foot applied for 5 minutes, the electrolyte being at 35 C.

Many members and structures may be provided with the electrodeposited black coatings of this invention. Thus, parts of electrical appliances, electronic devices and radia,

Small amounts of mineral acids are toleratediparito'f'vanadium. "The blackcoatings comprise"hoththe metals 'andthe oxides of "chromium and vanadium. Spec- "t'ros'co'pic and-other analysis shows that the vanadiu rfriis presentprimar'ilyfas vanadiumtr'ioxidexv og) with only a sm'all portion of Vanadium metal, fand'thatlthe chromium Tis:priniafilypresentas metal with oiily a small gpropor-w tionof chromium oxide. "-Inthe'black-coatingsof the chromium-vanadiuni-oxygen complex ithere are present 'fromlOO to"2 atoms of ichrornium per oxygentatom corn- "hine'd' therewith. t 7 It is intended {that i all matter I claim'as'myinverition;' I a I a 'lrAn aqueous electroplating.lectrolyte comprising "acid, {from 1.8 to "10 grams per "liter .oftvana'dium in soluble compound form, there'tbing present ffrom 0 to925 parts by weight of chromium perpa'rtof vanadium, V

7 contained in ille above 1 'idescriptionheiieeme'd -tofbe illustrative and not flimiting. r 1

essentially from T150'f'toi3'85 -grams ,per liter of chronic and from 3 to grams per liter of a "water solrilile carboxylic acid. t t 2. .An 1.aqueous electroplating electrolyte comprising essentiallyffr ofrn 15 :0 to 3.85 grams ,perflliter of-chromic acid, from 4 to 523 :grarnsper liter of'arnmoniurn vanadate,

, and from 3 to ,20 grams per liter of a carboxylic vacid selected fromthe ,group consisting ,of'ac/etic acid, :citric acid,tformic acid, oxalic acid and;propionic;=acid.

2,824,829 j J 1 t. j

3. In the process of electrodepositingan adherent highprising making the member a cathode in an aqueous electroplating electrolyte comprising essentially from 150 to t 385 grams per liter of chromic acid, from 1.8 to .10

grams per liter of vanadiiirni'n *soluble'compound form, there being ipreserit from 100 to $95531? lvliglit of per liter of a Water soluble carboxylic a'ififiand passing a plating electrical current :through the member atg a" 7 'foot, the electrolytebeing maintained at astemperature 'of from 30 C. to C. V r

4. A member having on-itsisurface anadherent, highly heat resistant, black c'oatin'g'consisting of chromium, vanadium and oxygen,-the vanadiun1 being present pri- 'marily as vanadium trioxide andrthe chromium, primarily as metallic chromium with a minor proportion of chromium oxide, "there be'ing atotal :of :from I atomsof chromium perflatomrof oxygen 'conrbined;there-' with, and from .100 ,-to 9; 5 partsby weight of-iihromium ,per'partby weight or vanadium. a a

References Cited in the fileof this paterit OTHER REFERENCES Jones: RowderMetallurgy, 1943, pp. 1: 

3. IN THE PROCESS OF ELECTRODEPOSITING AN ADHERENT HIGHLY HEAT-RESISTANT BLACK FINISH ON A MEMBER, THE STEP COMPRISING MAKING THE MEMBER A CATHODE IN AN AQUEOUS ELECTROPLATING ELECTROLYTE COMPRISING ESSENT IALLY FROM 150 TO 385 GRAMS PER LITER OF CHROMIC ACID, FROM 1.8 TO 10 GRAMS PER LITER OF VANADIUM IN SOLUBLE COMPOUND FORM, THERE BEING PRESENT FROM 100 TO 9.5 PARTS BY WEIGHT OF CHROMIUM PER PART OF VANADIUM, AND FROM 3 TO 20 GRAMS PER LITER OF A WATER SOLUBLE CARBOXYLIC ACID, AND PASSING A PLATING ELECTRICAL CURRENT THROUGH THE MEMBER AT A CURRENT DENSITY OF FROM 400 TO 2,000 AMPERES PER SQUARE FOOT, THE ELECTROLYTE BEING MAINTAINED AT A TEMPERATURE OF FROM 30* C. TO 50* C.
 4. A MEMBER HAVING ON ITSS SURFACE AN ADHERENT, HIGHLY HEAT RESISTAANT, BLACK COATING CONSISTING OF CHROMIUM, VANADIUM AND OXYGEN, THE VANADIUM BEING PRESENT PRIMARILY AS VANADIUM TRIOXIDE AND THE CHROMIUM PRIMARILY AS METALLIC CHROMIUM WITH A MINOR PROPORTION OF CHROMIUM OXIDE, THERE BEING A TOTAL OF FROM 100 TO 2 ATOMS OF CHROMIUM PER ATOM OF OXYGEN COMBINED THERE WITH, AND FROM 100 TO 9.5 PARTS BY WEIGHT OF CHROMIUM PER PART BY WEIGHT OF VANADIUM. 